Re: Best cap size for a sync gap

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: Terry Fritz <teslalist-at-twfpowerelectronics-dot-com>

Hi Malcolm,

Its speculation!!  Some NSTs have air gaps and others have the shunts 
crammed in pretty tight metal to metal.  Indeed, ones with air gaps should 
not saturate and would theoretically be poor candidates for an SLTR 
coil.  But the whole saturating thing is just an idea without proof.  If 
one were good, one could find an NST and work out all the areas, core 
types, magnetization curves, ... to see if the idea really has a basis in 
fact.  Pretty simple stuff for those that know the art of transformer design.

Cheers,

         Terry


At 03:55 PM 5/3/2004, you wrote:
>Does anyone here have *proof* that the NST shunts are saturating or
>is this just speculation? The reason I ask is that the shunts
>actually have an airgap in series with them. I can certainly imagine
>the main core approaching saturation.
>
>Malcolm
>
>On 3 May 2004, at 8:20, Tesla list wrote:
>
> > Original poster: Kurt Schraner <k.schraner-at-datacomm.ch>
> >
> > Hi Gary, Terry, all,
> >
> > the subject of best cap size for a sync gap and SLTR is stimulating,
> > and I like to add my SFr.0.01 to the interesting thread. Seeking a
> > well sized LTR value for my little coil UBTT (Uni-Bern-Tesla-Twin) and
> > a reply to Dan McCauley's overvolting question, I performed 29 SPICE
> > simulations, mentioned in my TCML posting of last September:
> >
> > http://www.pupman-dot-com/listarchives/2003/September/msg00311.html
> >
> > The sim's were for just for the _linear case_, where the NST
> > parameters (measured before) would not dynamically change. Meanwhile
> > the coil has been realized, and the calculated results, though in nice
> > agreement with reality otherwise, have taught me a different lesson:
> > The NST is indeed a more complex animal, than many of us might have
> > thougt before ;-). I experienced, and fully agree with those,
> > assigning magnetic shunt/core saturation in NST's a significant role
> > in TC use.
> >
> > The experimental results, compared to the simulation, were as follows:
> > In simulation a 230V/50Hz line power draw of ~880W / 1700VA
> > (PF=0.52)at an ~optimal setting of the rotary firing time of 4.2ms was
> > obtained. The experiment was showing 1300W / 1610VA (PF=0.807) at a
> > rotary setting of 3.6ms. No humming of the NST was heard, because of
> > the 1.5m-spark noise. The operation is stable and reproducible.
> >
> > The TC is powered by a 15/60 NST of Italian company FART. The SRSG
> > motor is fed via a phase-shifter of the John Freau type. The
> > phase-shifter can also be used to smoothly adjust the power input to
> > the coil. However I was scared adjusting the phase angle to the
> > predicted optimal 4.2ms, because of beginning safety-gap firing (2
> > brass balls of 0.5cm, adjusted ~10mm). A scope-shot of the charging
> > cycle at lower power may be had at:
> >
> > http://home.tiscalinet.ch/m.schraner/UpriC_oszi1304.jpg
> >
> > The charging circuit resonance, assuming linear behavior of the 15/60
> > NST (L.leak ~795H) and a 33nF primary cap would be about 31Hz. If
> > saturation brings the leak inductance down to 307H (38% of linear),
> > the cap would again be resonant! My 1300W operation of the NST might
> > imply a
> >      leak inductance of about 551H (69% of linear), leading to 37Hz
> > resonance - yet away from 50Hz, but the primary LTR cap value only
> > being ~1.8*Cresonant. Sooo... this alone shows SLTR experimenting
> > implies some risk, and should be performed cautiously. There certainly
> > are other effects, interwoven with the magnetically nonlinear behavior
> > of the NST. More thoughts, or even better: experimental info, would be
> > very welcomed to be seen appearing on this great list ;-).
> >
> > Data of the little UBTT may be supplied in a later posting, if of
> > interest. Two spark snapshots are here:
> >
> > http://home.tiscalinet.ch/m.schraner/1.06m_1332kl.jpg
> > http://home.tiscalinet.ch/m.schraner/TeslaAnVorlesung3kl.jpg
> >
> > The first pic shows operating the TC in single mode, in my lab; the
> > second in twin-mode at the Physics Institute of the Bern University,
> > during a lecture (sparklenghts: 1.06m and 1.3m respectively).
> >
> > Best regards,
> >                   Kurt
> >
> >
> >
> >
> >
> >
> >